1. Field of the Invention
The present invention relates to a digital, electronic, still camera for use with a memory card including a volatile semiconductor memory and a battery built therein for a data backup preserving data stored in the memory wherein image data representing an image of a subject shot by the camera is recorded in the volatile semiconductor memory.
2. Description of Related Art
A digital, electronic, still camera (or a digital still, video camera) is used to shoot a subject by a solid-state electronic imaging element such as a charge coupled device so as to attain a video signal thereof. The video signal is then converted into digital data to be recorded in a memory card; more specifically, in a semiconductor memory disposed therein for storing image data. The semiconductor memory card is implemented by a volatile memory such as a random access memory in most cases and hence inevitably requires an operation power to be supplied thereto. To this end, the memory card is provided with a memory backup battery (a cell) built therein. When the battery is used up, image data accumulated in the memory is lost. Consequently, it is essential to conduct a voltage check for a voltage of the battery.
On the other hand, there have been broadly used digital, electronic, still cameras in various fields and plural kinds of memory cards have been put on the market. This implies that the number of kinds of available memory cards will be increased in the future. Depending on a selected memory card type, there are respectively determined, for example, the type, capacity, access time, manufacturer, pin arrangement, and production date of the main memory and kinds of electronic apparatuses for use therewith. To cope with such situations, it has been proposed, for example, in the Japanese Patent Laid-Open No. 64-44556/1989, to beforehand load a non-volatile memory of a memory card with data related to compatibility thereof as listed above.
To conduct a (battery) check on a memory backup battery disposed in a memory card, a threshold voltage is beforehand decided as a reference of judgement for availability and replacement of the battery. The threshold voltage may possibly vary depending on the memory card type. Namely, when only a kind of threshold voltage is available, the battery check cannot be achieved for many kinds of memory cards. Moreover, there has not been materialized a digital, electronic, still camera which can sense a decrease in the built-in battery voltage for many kinds of memory cards.